Only Interactive.js used it.

Otherwise, special characters (e.g. `+`) in the idaSystemURL will be
interpreted as encoded data and converted to spaces. Which means that, say,
`git+https` will end up as `git https`. And then Bad Stuff (tm) happens.

Per https://reactjs.org/docs/introducing-jsx.html#specifying-attributes-with-jsx.
Fixes broken links on the IDA page.

- Use the singular (you can only select one from each list; you can't select
  "workflows");
- Simplifying wording (nobody needs to see “ESFRI” here!).

These services are not all JupyterHub systems. Indeed, at time of writing the
only service we've actually configured in esap-api-gateway is MyBinder, which
isn't a JupyterHub at all. Calling them “jhub” or similar is going to cause
confusion.